COMP Report: A survey of radiation safety regulations for medical imaging x-ray equipment in Canada.

X-ray regulations and room design methodology vary widely across Canada. The Canadian Organization of Medical Physicists (COMP) conducted a survey in 2016/2017 to provide a useful snapshot of existing variations in rules and methodologies for human patient medical imaging facilities. Some jurisdictions no longer have radiation safety regulatory requirements and COMP is concerned that lack of regulatory oversight might erode safe practices. Harmonized standards will facilitate oversight that will ensure continued attention is given to public safety and to control workplace exposure. COMP encourages all Canadian jurisdictions to adopt the dose limits and constraints outlined in Health Canada Safety Code 35 with the codicil that the design standards be updated to those outlined in NCRP 147 and BIR 2012.

Do natural enemies explain fluctuations in low-density spruce budworm populations?

Understanding the causal pathways through which forest insect outbreaks are triggered is important for resource managers. However, detailed population dynamics studies are hard to conduct in low-density, pre-outbreak populations because the insects are difficult to sample in sufficient numbers. Using laboratory-raised larvae installed in the field across a 1,000 km east-west gradient in Québec (Canada) over an 11-yr period, we examined if parasitism and predation were likely to explain fluctuations in low-density spruce budworm (Choristoneura fumiferana; SBW) populations. Parasitism rates by the two main larval parasitoid species, Elachertus cacoeciae and Tranosema rostrale, peaked during different years. This suggests that temporal fluctuations in overall parasitism were partly buffered by compensatory dynamics among parasitoid species. Still, spatial covariance analyses indicate that the residual interannual variation in parasitism rates was substantial and correlated over large distances (up to 700 km). On the other hand, interannual variation in predation rates was not spatially correlated. Piecewise structural equation models indicate that temporal variation in parasitism and predation does not influence temporal variation in wild SBW abundance. Spatially, however, SBWs installed in warmer locations tended to show higher parasitism rates, and these higher rates correlated with lower wild SBW population levels. Overall, the results indicate that large-scale drops in parasitism occur and could potentially contribute to SBW population increases. However, during the period covered by this study, other factors such as direct effects of weather on SBW larval development or indirect effects through host tree physiology or phenology were more likely to explain large-scale variation in wild SBW populations.

Pheromone-Based Monitoring of Spruce Budworm (Lepidoptera: Tortricidae) Larvae in Relation to Trap Position.

The local abundance of male spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), was evaluated in the province of Quebec at 112 locations between 2002­2012 using pheromone-baited traps deployed on lower branches near the ground level (GL) or in the tree canopy (TC; three traps at GL and TC for each location); in addition, the presence of second instars (L2) was assessed at each location on three balsam fir branches. Numbers of moths captured at GL and TC were highly correlated, and the regression parameters did not vary between years. Consequently, estimates of L2 based on pheromone trap catches are precise independent of trap location, and deploying traps at ground level (rather than in the tree canopy) does not come with a loss of accuracy in L2 assessments. Relationships between moths (x) and L2 (y) exhibited strong nonlinearity and were most adequately described by exponential functions of the form: ln (y+1)=[ß0+ß1×k ln (x)]. A conservative threshold of 100 males per trap at GL (corresponding to one L2 per branch) may be used to guide forest managers in the transition from endemic to epidemic populations. Relationships between L2 and moths are likely influenced by the number of traps per site; hence, the tentative threshold above is only valid for jurisdictions relying on three traps per site. Considering the economic importance and rising populations of spruce budworm, rigorous quality control programs must be implemented promptly to ensure a steady supply of standardized pheromone lures across years.

Derivation of Pheromone-Based Larval Thresholds in Spruce Budworm Accounting for Distance to Defoliated Forest Stands.

Spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is the most severe defoliator of Pinaceae in Nearctic boreal forests. Three tools widely used to guide large-scale management decisions (year-to-year defoliation maps; density of overwintering second instars [L2]; number of males at pheromone traps) were integrated to derive pheromone-based thresholds corresponding to specific intergenerational transitions in larval densities (L2i → L2i+1), taking into account the novel finding that threshold estimates decline with distance to defoliated forest stands (DIST). Estimates of thresholds were highly variable between years, both numerically and in terms of interactive effects of L2i and DIST, which limit their heuristic value. In the context of early intervention strategy (L2i+1 > 6.5 individuals per branch), however, thresholds fluctuated within relatively narrow intervals across wide ranges of L2i and DIST, and values of 40-200 males per trap may thus be used as general guideline.

Bivariate Pheromone-based Monitoring of Spruce Budworm Larvae (Lepidoptera: Tortricidae).

A bivariate approach to pheromone-based monitoring is developed for the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae). The approach uses captures of males at pheromone traps for generation t (♂t) as a transitive term between densities of overwintering larvae in consecutive generations (L2t, L2t+1), based on a large data set including >2,000 observations in the province of Quebec (QC) between the interval 1992 and 2010. Although estimates of L2t and ♂t are autocorrelated to some extent, multi-year assessments of larval densities combined with pheromone trapping are justified by the complementarity (statistical significance) of both L2t and ♂t in predicting L2t+1 for 15 of 18 pairs of 2-yr intervals. Bivariate pheromone-based thresholds (number of males corresponding to specific transitions in larval densities between L2t and L2t+1) are reported for each year. As expected, thresholds for stable populations (L2t = L2t+1) were lower than for populations with positive growth rate (L2t < L2t+1). The thresholds derived in this study have limited heuristic value; however, because they vary greatly from year to year.